Tungsten-inert gas welding, arc gas welding, beam welding, and the like, are widely employed as methods of connecting pipes and fluid parts, such as valves, regulators, and the like, which are employed in fluid supply pipe systems. However, in this conventional welding technology, the surface roughness of the welded portions, and the deposition of metal on the inner surfaces of supply system pipes as a result of metal fumes released from the fused portion, have not been considered. In particular, in conventional gas supply pipes or parts having welded portions, no treatment was made with respect to the deposition of metal fumes generated by welding on the inner surfaces of supply system pipes, so that on contact with extremely active special material gasses, these deposited metals tended to corrode and be separated. As a result, the use points, such as semiconductor manufacturing devices and the like, which employed gasses were subject to metal contamination, and this has been recognized as an important factor blocking an increase in performance of such semiconductor devices. Furthermore, while no problems occurred over short periods of time with respect to inert common gasses, it has been discovered by the present inventors that there are some problems with reliability over longer periods.
The deposition of metal fumes as a result of the welding of fluid and gas supply pipe systems, and the surface roughness of the welded portions, will be explained in greater detail using FIG. 4. FIG. 4 shows welded portions in which pipe materials are welded by means of tungsten-inert gas welding. In the figure, reference 401 indicates a tungsten electrode, while reference 402 indicates pipe materials which are subjected to welding. Reference 403 indicates a welded portion, while reference 404 indicates metal fumes which are released from the fused portion. These metal fumes 404 are carried by the arc gas or back seal gas flow and are deposited on the surface of the pipe material 402 at the downstream side of welded portion 403, and become deposited metals 405. These deposited metals 405 do not present the problem of separation with respect to inert gasses; however, when a corrosive gas, for example, hydrogen chloride gas, is caused to flow, the deposited metals 405, which are not bonded to the surface of the material, but are merely deposited thereon, are subject to separation. The separating metals comprise Fe, Ni, Cr, and Mn, which are chiefly contained in the metal materials, and because these metals exert a great influence on the LSI characteristics, the removal of these metals is a crucial problem in semiconductor production.
However, in installation methods for fluid supply pipe systems, such as current semiconductor production apparatuses or the like, there has been no effective removal of the above metal contaminants, and there has been, in particular, a great desire for a welding system which can be applied to apparatuses requiring a highly clean atmosphere.
The present invention was created in light of the above circumstances; it has as an object thereof to provide a welding system for super high purity fluid supply pipe systems which is capable of easily and completely removing metals deposited at the vicinity of the surface of the welded portion and at the inner portions of the fluid supply system, during the installation of a super high purity fluid supply pipe system, and which is furthermore capable of setting up a super high purity supply system in a short period of time.